Forget the polls. When Chelsea Clinton – in her first true campaign event of this presidential season -- is attacking Bernie Sanders on health care, you know the Clinton campaign thinks they’re in a closer race than they might have ever imagined. (Chelsea campaigned plenty in ’08, but we don’t ever remember her throwing these kinds of jabs at Barack Obama or John Edwards.) “I’m working hard, and I intend to keep working as hard as I can,” Hillary Clinton said on “Today” this morning when NBC’s Savannah Guthrie asked her about the tightening polls. “I am excited where we are.” And Clinton continued to criticize Sanders on guns and health care. “We shouldn’t be ripping up Obamacare and starting over,” she said, referring to Sanders’ proposal for a single-payer system. We’re now less than 20 days from Iowa, and Team Clinton is certainly feeling the pressure.

Three possible explanations for the tightening Democratic race

So what happened in the span of two weeks after the Christmas/New Year’s break to change what was a STABLE Democratic race, especially after Joe Biden said he wasn’t running, to an INCREDIBILY CLOSE contest between Clinton and Sanders? Here are three theories:

The Enthusiasm Factor: Voters are just now being to tune in, and the candidate who has the excitement/enthusiasm advantage – Sanders – is benefitting;

The Trump Factor: So what changed between Christmas and now? Donald Trump starting attacking Bill and Hillary Clinton over Bill’s past sexual history. Did those attacks move Democratic numbers? Did the “hard to measure” issue of “Clinton fatigue” kick in with some Democrats who are picking Bernie over fear of returning to the old dramas of the ‘90s?

The Anti-Establishment Factor: Think about it: Both Barack Obama and Republican responder Nikki Haley admitted that politics is broken in Washington, and that their side deserves some of the blame. When there’s that admission, it’s not surprising why Trump and Cruz are leading on the GOP side, and why Bernie Sanders has the momentum in the Democratic contest. Sanders is the most anti-establishment on the Dem side and Clinton has the establishment brand.

But there is a silver lining for Clinton: A win in Iowa -- any win -- will look more impressive than it did a month ago. As Greg Sargent writes, it could be a good thing for Democrats that Clinton actually has to fight to win the nomination – rather than coast to victory. We’ll see. It’s quite remarkable that a 74-year-old senator who was always written off as a bit of a gadfly has turned into the Democratic Party’s latest progressive heartthrob (when he’s never even been a Democrat until now). Is that a reflection on Bernie or Hillary?

As for President Obama’s State of the Union speech last night, it’s hard to disagree with the take from MSNBC’s Benjy Sarlin and Alex Seitz-Wald. “In many ways, the speech functioned as a point-by-point rejoinder to the long list of attacks Republican candidates have levied against his administration during the presidential race. It was almost as if, after a yearlong Friars Club Roast, the president finally got to take the podium and rebut his tormentors. ‘[A]ll the talk of America's economic decline is political hot air,’ Obama said at one point. ‘So is all the rhetoric you hear about our enemies getting stronger and America getting weaker.’” Sarlin and Seitz-Wald add, “But there was a deadly serious undercurrent to the speech, especially when it turned to the politics of Trump, whose rise appears to have genuinely shaken the president. Without ever mentioning his name, Obama repeatedly decried the billionaire's hostile rhetoric and proposals regarding immigrants and Muslims as an empty, misguided and un-American response to the challenges faced by the country at home and abroad.” There are two perceptions of America right now, and they are dramatically different: 1) The GOP perception is very dark and fear of things getting worse (a perception being fed as much by stagnation on the ground where many GOP voters live); 2) The Dem perception is more optimistic as the economy is getting stronger in many places where Dems live. Point is: Both sides don’t believe the other even lives in the same country… Maybe they don’t.

Nikki Haley admits she was criticizing Trump in her State of the Union response

It’s not every day when the person who delivered the Republican Party’s State of the Union response ADMITS he/she was criticizing the current GOP presidential frontrunner in the speech. But that’s exactly what happened on “Today” this morning. When NBC’s Matt Lauer asked SOTU responder Nikki Haley if she was referring to Donald Trump when she said this last night -- “During anxious times, it can be tempting to follow the siren call of the angriest voices -- Haley answered in the affirmative. “He was one of them, yes.” Wow. As for the GOP reaction to Haley’s speech, the moderate/establishment wing of the party loved it, while the insurgent/outsider wing hated it. And if you want to see how today’s Republican Party might be breaking into two, the praise-vs.-criticism that Haley received is a good place to start. By the way, Haley ensured that her endorsement in South Carolina’s GOP primary is going matter -- and that it’s probably not going to Donald Trump or Ted Cruz.

Des Moines Register poll: It’s Cruz and Trump -- and then the rest

As for Trump and Cruz… This morning’s brand-new Des Moines Register/Bloomberg poll, considered the gold standard of Iowa polling, almost mirrors the latest NBC News/WSJ/Marist Iowa poll released on Sunday. The DMR survey has Cruz at 25%, Trump 22%, Rubio 12%, and Carson at 11%; all other Republicans get less than 5%. NBC’s Hallie Jackson notices in the poll that 83% of GOP voters said the so-called “birther” issue regarding Ted Cruz doesn’t bother them. But NBC’s Vaughn Hillyard points out that 42% find Cruz’s stance on phasing out the ethanol subsidy to be unattractive, versus 37% who say it’s attractive. So it’s entirely possible that the ethanol story – not the birther charges – is the more damaging to Cruz. The Des Moines Register says the Democratic numbers are coming out tomorrow morning.

The Trump-Cruz bro-mance is officially over

Also, it’s worth pointing out that the Trump-Cruz bro-mance is officially over. Here’s NBC’s Hallie Jackson (and one of us): “The truce is no more... In an interview on the Howie Carr radio show Tuesday, Cruz suggested that Trump should play ‘New York, New York’ at his rallies – rather than ‘Born in the USA,’ which Trump has recently started airing as a clear dig at Cruz’s Canadian birthplace. ‘I think he may shift in his new rallies to playing “New York, New York” because Donald comes from New York and he embodies New York values,’ Cruz said. ‘And listen, The Donald seems to be a little bit rattled.’” Folks, this is a big deal, because Trump and Cruz trading attacks over the next three years is a relief to the establishment candidates.

Pundits and politicians, raise your hand if you overreacted to yesterday’s Iran news

One final point to make: A lot of people OVERREACTED to yesterday’s news that 10 Americans were captured by the Iranians. As NBC’s Jim Miklaszewski reported this morning, those Americans are back at the U.S. Navy base in Bahrain, and the Iranians said they saw no evidence of espionage. The Obama administration and its allies are arguing that five years ago -- before the Iran deal -- this would have been a much more complicated showdown between the U.S. and Iran. And it’s hard to disagree with that assessment. Yesterday was a reminder of how campaign season can take a minor diplomatic flare up and escalate it rhetorically to, well, ridiculous heights. Perhaps folks should take a deep breath and wait for facts to support their rhetoric.

On the trail

Donald Trump holds a campaign rally in Pensacola, FL at 7:00 pm ET… Bill Clinton makes three stops on behalf of his wife in New Hampshire… Ted Cruz, Marco Rubio, and John Kasich are in South Carolina… Chris Christie stumps in New Hampshire… And Mike Huckabee and Rick Santorum are in Iowa.